This invention relates generally to the field of tube bending devices which utilize a reciprocating ram member to move a bending shoe relative to two fixed workpiece holding rollers. More particularly, the invention relates to such devices capable of imparting a bend in the tubular workpiece of up to 180 degrees.
Apparatus for cold bending tubes or pipes are well known in the art. A typical device incorporates a bending shoe mounted onto a reciprocating ram or piston, the ram being advanced either mechanically or hydraulically. The bending shoe has a semi-circular configuration on the forward portion of its workpiece meeting face and parallel straight portions extending behind the semi-circular portion, with a workpiece receiving channel concave in cross-section extending around the workpiece meeting perimeter in a U-shape. A pair of workpiece holding rollers are mounted in a fixed relation to the bending shoe, one on each side of the bending shoe. Each roller has a receiving channel concave in cross-section for holding the tubular workpiece. The bending channel in the bending shoe and the receiving channels in the rollers are semi-circular in vertical cross-section and are sized to match the outer diameter of the tubular workpiece being bent in the device, with the channel not exceeding one-half the diameter of the tube in depth. The rollers are fixedly mounted on a base or other housing member such that the outer lips of the straight portions on each side of the bending shoe contact the outer lips of each of the rollers when the bending shoe is advanced between the two rollers. In this manner the bending shoe channel and the roller channel will completely encircle the tube being bent 180 degrees, thus preventing crimping or folding of the tube.
Examples of such devices are shown in U.S. Pat. No. 2,880,779 to Mingori and U.S. Pat. No. 3,018,818 to Swanson. Other known devices for bending tubes use a fixed bending shoe and reciprocating rollers, such as is shown in U.S. Pat. No. 3,073,372 to Lang. A problem often occurs in these devices, especially when bending tubes made of relatively soft metal or of small diameter, in that crimping or folding occurs at the central bending point. This can occur if the tube moves sightly away from the bending shoe during the operation, in which case the lip of the semi-circular receiving channel no longer encases the tube to its center line. One solution to solve this problem is shown in U.S. Pat. No. 4,005,593 to Goldberg. This device incorporates a clamp which is positioned at the apex of the bending shoe, thus completely encircling the tube being bent at the central bending point.
This invention addresses the problem of preventing crimping in small tubes during cold bending without requiring an extra attachment to be affixed to the bending apparatus. It has been discovered that extending the lip of the receiving channel on the bending shoe in the area of the bending apex prevents crimping resulting from separation of the tube from the channel. The extended lip is not maintained around the full 180 degree face of the bending shoe, but is truncated on both sides so that there is no extension of the lip at the straight side portions. This allows the lips of the holding rollers to make contact with the lips of the bending shoe along the side portions in order to completely encircle the tube when the tube is fully bent.
It has also been discovered that the problem of crimping can be overcome by utilizing channels in the bending shoe and rollers which are slightly smaller in size than the outer diameter of the tube being bent, rather than matching the outer diameter of the tube as is commonly practiced. The pressure against the tube during the early advancement of the bending shoe ram forces it to adapt to the smaller diameter of the channel, imparting compressive forces in the region of the tube undergoing the bending deformation.
To accommodate tubes of different sizes, it is necessary that the bending shoe and rollers be detachable to allow selection of elements having the correctly sized channel to match the particular tube diameter. It is also necessary to provide multiple mounting positions for the rollers on the housing or base plate to account for both the tube size and the degree of bend desired. The common solution for mounting the rollers is to provide a number of apertures at selected locations to correspond to particular pipe sizes. This is an obvious drawback in that the user is limited to the predetermined positions. Should the user need to custom bend a pipe a certain number of degrees over a given range, the apparatus may not have the proper apertures for positioning the rollers correctly.
To solve this problem, the invention comprises two continuous slots cut into the baseplate or housing, one corresponding to each roller. Thus each roller can be positioned at any point within the slot, so that the device is usable to bend a tube into any desired arc.
It is an object of this invention to provide a tube bending apparatus suitable for bending small or soft material tubing up to 180 degrees without crimping, the improvement being an extended lip on the workpiece receiving channel on the forward portion of the bending shoe.
It is a further object to provide such an apparatus where the workpiece holding rollers are positionable over a continuous range of positions rather than at predetermined locations.
It is a further object of the invention to provide such an apparatus where the inner diameter of the receiving channel on the bending shoe is slightly smaller than the outer diameter of the tube being bent.